The existing precision rotational transmission mechanisms are widely used in the fields of solar power generation apparatuses, radar antenna positioning apparatuses and the like, and most of the precision rotational transmission mechanisms adopt gear pairs, ball screw pairs and other transmission forms. In order to satisfy a requirement of outputting a large enough torque, and consume power of a motor as low as possible, a total transmission ratio of a transmission apparatus needs to reach tens of thousands. To satisfy such a large transmission ratio, for gears, ball screws and other transmission forms, multi-stage transmission is required, and the number of single-stage meshing gear teeth must differ greatly to satisfy the large transmission ratio, thereby seriously affecting the service life of the gears and making a whole structure very complicated and huge. From use conditions, the gears, the ball screws and other transmission forms generally do not apply to conditions of very bad weather environments, such as a solar power transmission apparatus applied to a harsh field environment, in which the harsh field environment presents a tough test to precision of a second transmission mechanism and the service life of a transmission component. As a solar power generation tracking apparatus, little shaking of a heliostat may cause large deviation of reflected light, so high requirements are put forward to return difference of an output shaft of the transmission apparatus. The gear form mainly adopts adjustable small backlash gears or variable tooth thickness gears, but the single-stage transmission is relatively small, so it is difficult to satisfy overall design requirements of the large transmission ratio. Adjustment of a ball screw transmission clearance needs to increase a pre-tightening force, thereby increasing friction, reducing transmission efficiency, accelerating the friction of a screw, and shortening service life. The existing precision rotational transmission mechanism generally includes the second transmission mechanism, a vertical second transmission mechanism, a fixing support and a connecting part. Due to complicated structures and large volumes of the second transmission mechanism and the vertical second transmission mechanism, this inevitably results in a larger volume and a more complicated structure of an overall mechanism (e.g., the patent, with an application number of 200980132680.X and titled ‘a gear transmission apparatus and a solar power generation apparatus using the same’, discloses a precision rotational transmission mechanism adopting gear transmission, but a driving shaft of the precision rotational transmission mechanism adopts the gear transmission, and an output end is just a shaft 110 end; thus, a cross-sectional area of the output shaft is just a small part of the apparatus, thereby resulting in insufficient rigidity, weak impact resistance and short service life.).